1. Field of the Invention
This invention relates to a filter device, and more particularly to a filter cartridge which is used in a liquid or gas filter. Still more particularly, the present invention relates to a filter cartridge which employs granulated material such as activated carbon as a filtering material. Such filters are typically used with aquariums.
2. Description of Related Art
FIG. 1 illustrates one prior filter cartridge design which includes a substantially planar back structure or frame 20 having a peripheral section 20a and a slightly indented central section 20b. A plurality of elongated parallel channels 22 are integrally formed in a back wall 23 of the back frame 20. As best seen in FIG. 3, the back wall 23 has a generally serpentine cross-section to define the channels 22. Alternatively, a back structure may define the channels by a plurality of horizontal shelves 23a as shown in FIG. 4.
Disposed within the channels are filter granules 24 such as activated carbon. Typically, enough granules are employed to substantially fill each of the channels 22 as shown in FIGS. 2-4. Each of the channels 22 includes a plurality of openings 26 which enable water to flow through the back frame 20. The openings 26 are generally smaller than the carbon granules 24 so that the granules cannot pass through them.
The filter granules are typically placed into the channels 22 when the cartridge is oriented horizontally. A sheet-like filter element 28 is then secured to the back frame 20 and serves to retain the carbon granules 24 within the channels 22 in use. Typically, the filter element 28 is secured only at the periphery 20a of the back frame and is attached by means of a heat bonding process. The purpose of the filter element 28 is to filter out large particulate matter from the water passing through it. The granules 24 operate as a chemical filter to chemically treat other pollutants. It is also known to secure a second filter element 30 to the back side of the back frame 20. This element will provide some additional filtration. However, most of the large particulate filtration will be provided by the front filter element 28.
With the filter element 28 in place, it is intended that the granules 24 be retained within their respective channels 22. However, because the material of the filter element 28 is often quite flexible, some of the granules 24 may fall out of their channels, particularly if the filter is subjected to vigorous handling during installation or shipping. If too many granules fall toward the bottom of the filter cartridge, water passing through the upper portion of the cartridge may not receive sufficient chemical filtration, thereby reducing overall filtration efficiency.
After prolonged use, the filter element often comes clogged with debris and the filter cartridge comes relatively heavy and very slippery. As a result, it can be a difficult and unappealing task to remove the filter cartridge from the filter box in order to replace it with a fresh filter cartridge.
In addition, as the filter element becomes clogged with debris, the water level can increase behind the filter cartridge to the point that water overflows the filter box. This can result in partially emptying the aquarium and spilling aquarium water on the floor. Besides the mess, water flow to the aquarium can also be stopped or reduced to a point that adequate aeration of the aquarium water is interrupted which can be harmful and even fatal to the fish in the aquarium.
To provide an indication that the filter cartridge needs replacing or servicing, it is known to provide a clogged filter indicator. Typically, such indicators take the form of an overflow indicator in which the flow of water is diverted in some manner to indicate a clogged filter. However, until the filter is replaced or serviced, the flow of water to the aquarium may remain so impaired as to reduce the aeration of the water in the aquarium to harmful levels.